Psychophysical and behavioral studies with humans and non-verbal animals have lead researchers to propose that many natural sugars, a subset of amino acids, and some synthetic compounds produce qualitatively indiscriminable percepts. Recently, it has been suggested that in taste cells a family of receptors called the T1Rs mediates signal transduction of these "sweeteners." However, not all of these compounds bind with the same receptor in this family, providing a possible neural basis for discriminability. The experiments proposed here are designed to explicitly test the ability of mice to distinguish between sucrose, glucose, glycine, L-serine, L-alanine, and D-trytophan in operant taste discrimination tasks. The proposed experiments will help characterize the qualitative similarities and differences between these taste stimuli and thus provide data critical in constructing a qualitative perceptual space related to these "sweeteners" in this important animal model. As such these behavioral experiments will provide a functional context to guide the interpretation of findings from more molecular levels of analysis. [unreadable] [unreadable]